Age Invariant Regime for Multi-Source Content Update in Mobile Opportunistic Networks

In the multi-source content update scenario where each mobile node can be both a publisher and subscriber and opportunistic contacts are used for spreading out up-to-date contents, the age of contents would be the main interest in performance evaluation. We can simplify the overall age dynamics in this scenario by two parameters, which are content update rate and contact rate among mobile users. In this paper, we analyze how the age of time-evolving contents changes in publish/subscribe scenario when Poisson update and contact are assumed, and show that there exists an age-invariant regime where the average age does not depend on content update rate or contact rate. We also compare the age-invariant regime in publish/subscribe scenario with that of service provider content update case, and show a stark contact in those regimes. Then, we extend our study into existing mobility models that generate non-Poisson contacts, show that there still exists an age-invariant regime where Poisson assumptions suffice to capture the age dynamics, and specify a general rule of thumb that decides the scope of this regime. Our work that shows the existence of an age-invariant regime is in sharp contact to previous works that highlighted the impact of mobility models under single message scenario.